cer.by is powered by Polr, an open source, minimalist link shortening platform. Learn more at its Github page or its project site.
Polr is licensed under the GNU GPL License.

The GNU General Public License v3
Copyright (C) 2013-2015 Chaoyi Zha, the Polr Project
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program. If not, see http://www.gnu.org/copyleft/gpl.html.